Katosi Water Treatment Works: Secant Wall, December 2019
Scope of Services:
Construction of a secant pile wall cofferdam for a raw water intake at Katosi Water Treatment Works in Mukono District. The completed cofferdam was 10m deep and retained both soil and water from Lake Victoria to facilitate the installation of a pump house for the water treatment works. A total number of 122 piles of 800mm and 1000mm diameters were installed to 18m depth by the rotary bored method within a period of one and a half months.
Location: Katosi, Mukono District, Uganda
Completion Date: December 2019
Main Contractor: Sogea Satom
Client: National Water and Sewerage Corporation (NWSC)
Project Description:
The National Water and Sewerage Corporation (NWSC) awarded the contract for the design and construction of a Water Treatment Plant (WTP) in Katosi to international contractors Sogea Satom. Situated on the shores of Lake Victoria, the Katosi WTP will supply potable water to the capital city of Kampala. As part this major infrastructure programme, EA Piling was selected to provide a specialist temporary works package for the water intake structure.
Sogea Satom approached EA Piling, requesting a technical solution for the construction of a cofferdam measuring 17m by 17m on plan and 10m in depth. The cofferdam would have to be water tight in order to facilitate the installation of pumping machinery and associated equipment for the water intake works.
Having considered all of the viable options, EA Piling opted for a secant pile wall cofferdam to safely retain the 10m of both soil and water required by the client. In consultation with specialist geotechnical engineers, the secant wall was designed using a combination of 800mm and 1000mm diameter rotary bored piles, installed to a maximum depth of 18m. EA Piling’s final proposal fulfilled client requirements whilst remaining cost-effective.
Shortly after signing the contract the Soilmec R620 piling rig was mobilised to site from Kampala. Temporary casings were used throughout the piling works to prevent the bored holes from collapsing.
EA Piling ensured the piling platform was adequate to perform the works in a timely and safe manner. Concrete was batched and delivered by the main contractor, Sogea Satom. Reinforcement cages were cut and tied by EAP on site and subsequently installed in the rotary bored piles.
As per the geotechnical investigations, site stratigraphy comprised superficial deposits of lake alluvium underlain by weathered rock. Despite this potentially challenging geology, EA Piling successfully installed the total number of 122 piles within a schedule of less than one and a half months.
EA Piling is looking forward to many more successful collaborations with Sogea Satom in the future.
